A mobile communication is often subject to fading which causes the level of a received signal to fluctuate depending on various radio wave propagation environments. An effective measure against this fading is antenna selection diversity. The antenna selection diversity is implemented normally by installing a plurality of antennas and carrying out communication by selecting an antenna with good conditions when a reception condition deteriorates due to fading. As such an antenna selection diversity apparatus, for example, those disclosed in Patent Documents 1 and 2 are conventionally known.
Patent Documents 1 and 2 disclose antenna selection diversity apparatuses based on a TDMA (Time Division Multiple Access) communication scheme time-sharing a common frequency by a plurality of users, which realizes diversity by sampling intensity of received signals through antennas during a time slot period irrelevant to a receiver and selecting an optimal antenna before receiving a time slot relevant to the receiver. An overview of such an antenna selection diversity apparatus will be explained below.
FIG. 1 is a block diagram showing a configuration example of a conventional antenna selection diversity apparatus. FIG. 1 shows an antenna selection diversity apparatus in a minimum configuration with two antennas. That is, the conventional antenna selection diversity apparatus 10 shown in FIG. 1 is provided with antennas 11, 12, a switch 13, an antenna duplexer 14, a reception section 15, a reception level measuring section 16, a timing control section 17, an antenna selection section 18 and a transmission section 19.
In such a configuration, the timing control section 17 controls timings for transmitting/receiving data, measuring antenna reception levels and selecting an antenna to realize antenna selection diversity, gives an antenna selection instruction to the antenna selection section 18 and a measurement instruction to the reception level measuring section 16.
The antenna selection section 18 causes the switch 13 to perform switching operation at the timing instructed from the timing control section 17. That is, the switch 13 selects the antenna 11 during a certain antenna reception level measuring time, connects the antenna to the reception section 15 through the antenna duplexer 14 or selects the antenna 12 during another antenna reception level measuring time and connects the antenna to the reception section 15 through the antenna duplexer 14.
As a result, the received signal at the antenna 11 and the received signal at the antenna 12 are input to the reception level measuring section 16 through the reception section 15. The reception level measuring section 16 measures the reception level at the antenna 11 and the reception level at the antenna 12 and sends both measured antenna reception levels to the antenna selection section 18.
The antenna selection section 18 compares the reception level of the antenna 11 and the reception level of the antenna 12 sent from the reception level measuring section 16, determines the antenna having the greater reception level as the antenna to be used during a data transmission/reception time and causes the switch 13 to select the antenna. The reception section 15 and transmission section 19 use the antenna selected by the antenna selection section 18 during a data transmission/reception time. Using this antenna selection diversity apparatus 10 makes it possible to carry out communication using an antenna suitable for a radio wave propagation environment, and is therefore expected to improve the communication performance.    [Patent Document 1] Japanese Patent Publication No. 2719575    [Patent Document 2] Unexamined Japanese Patent Publication No. 6-140971